Dieter wrote:
It appears that many HDTV sets display 1080p which they generate
internally (those with so-called 3:2 pull down have to do it) and all
flat panels are progressive (although most of them are currently 720
lines). Strange thing about 3:2 is that they don't display it at 48 fps
as theaters do (24 fps movie projectors have a two blade shutter to
avoid flicker)
If you display a 24 fps movie on a LCD, how do you avoid flicker?
Once a pixel settles into a new value, it just stays there constantly,
unlike a CRT where the phospher is constantly fading and being refreshed.
LCDs aren't fast enough (yet?) to simulate the double shutter they do
with film.
An LCD is on all the time so there is no flicker just the slight delay
when they are refreshed. The issue is to avoid the artifacts from
interlaced conversion of 24 fps film.
IIUC, an LCD TV is progressive scan and refreshed at 60 fps. So you
show one frame three times, the next one two times, the next one three
times, etc. and this adds up to 60 fps with a slight amount of stutter.
The easiest way to do this would seem to be exchange buffering.
The question that I have is how an LCD is updated. Does it update with
a (progressive) scan like a CRT or is it double buffered and updates the
whole screen at the vertical sync pulse? This is going to make some
difference in how a movie looks but there isn't anything that the
graphics board can do about it.
LCD computer monitors would present different frame rate issues. Many
of them are only 60 fps and would be treated just like TV, but there are
some that support higher vertical refresh rates. I would suggest that
we support 72 fps since this is 3 times the movie frame rate which would
display movies a little better than 60 fps since there would be no
stutter (each progressive frame shown 3 times).
This would also be good for CRTs and projection TVs. When you are
showing a small image on your computer monitor it doesn't make much
difference, but if somebody hooks up a HD DVD to their 42 inch (or
larger) 1080 HD set, we should be able to optimize this for the best
viewing.
With a computer monitor (that supported higher refresh rates), it would
be best for the user to select either 60 fps or 72 fps depending on
whether they were watching 24 fps filmed movies or 30 fps video media
(or the original print of Oklahoma).
--
JRT
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